What do you expect to happen when you put a good looking male and female lead on a closed film set for months on end?

Oftentimes, the close quality time together leads life to imitate art.

While some seemingly perfect romances only last a short time ("The Notebook" co-stars Ryan Gosling and Rachel McAdams), other more odd couple pairings, such as Humphrey Bogart and Lauren Bacall, have lasted nearly a lifetime.

And who can forget the Jennifer Aniston, Brad Pitt, Angelina Jolie love triangle? We can't. But we bet you forgot about the following 11 onset romances, so let us remind you...

LeAnn Rimes and Eddie Cibrian

Lifetime, Getty Images

Apparently Lifetime movies are more steamy than we all thought.

Eddie Cibrian and LeAnn Rimes initially met on the set of the made-for-TV movie, "Northern Lights" about a crime in a small Alaska.

But the real news happened offscreen.

Both Cibrian and Rimes were married during the filming of the movie and when rumors spread about the affair, Rimes would not confirm or deny while Cibrian, who has two children, flat out denied it.

Cibrian divorced his wife Brandi Glanville in 2009 and Rimes soon followed with Dean Sheremet in 2010. Once the couple married in 2011, Rimes confirmed the affair.

Russell Crowe and Meg Ryan

Warner Brothers, Wikimedia Commons

When America's romantic comedy queen Meg Ryan decided to venture into dramatic fare with 2000's "Proof of Life," she had been married to actor Dennis Quaid for 10 years.

Enter Russell Crowe.

Ryan and Crowe had an affair on set, causing Quaid to file for divorce. The new romance only lasted a few months.

Elizabeth Taylor and Richard Burton

Wikimedia Commons

One of the most famous onset affairs of all time was the tryst between Elizabeth Taylor and Richard Burton while filming "Cleopatra."

During production, Taylor was married to Eddie Fisher, who actually had an affair with Taylor while he was married to Debbie Reynolds.

Before the ink was even dry on her divorce papers, Taylor married Burton. The two had a tumult ous on and off relationship for years. The couple were married twice, from 1964-1974 and 1975-1976.

Ryan Phillippe and Abbie Cornish

Screenshot, Jason Kempin/ Getty Images

It seemed like a perfect marriage.

Ryan Phillippe and Reese Witherspoon looked so happy together after Witherspoon won an Oscar for "Walk the Line."

But when the couple separated, people were shocked and quickly rumors began floating around that Phillippe had supposedly cheated on Witherspoon with his "Stop-Loss" co-star Abbie Cornish.

Peter Bogdanovich and Cybill Shepherd

During the filming of Peter Bogdanovich's critically acclaimed "The Last Picture Show," the director cast a 21-year-old model/actress named Cybill Shepherd to play a young seductress.

Then life imitated art.

The director and Shepherd soon fell in love and Bogdanovich divorced his wife of nine years, Polly Platt, to be with the young actress.

The couple stayed together for six years and never married but are still friendly.

John Malkovich and Michelle Pfeiffer

Screenshot, Kevin Winter/ Getty Images

John Malkovich is ever the method actor.

Malkovich played lover to Michelle Pfeiffer on the set of "Dangerous Liaisons" which led to romance off the screen.

The affair was reported to have taken place while Malkovich was still married to actress Glenne Headley and the two later filed for divorce.

The Malkovich-Pfeiffer romance didn't last long and both moved on to artists behind the camera. Pfeiffer to her current husband, writer/producer David E. Kelley, and Malkovich to his longtime partner Nicoletta Peyran, who was the second assistant director on his 1989 film "The Sheltering Sky."

Billy Crudup and Claire Danes

Screengrab, Evan Agostini/ Getty Images

Before making the jump into big budget films like "Mission Impossible III" and "Watchmen," Billy Crudup was most notably recognized as the lead singer of Stillwater in "Almost Famous".

After making "Stage Beauty" however, no one was talking about his movie cred.

Crudup met Claire Danes on the set of the romantic period piece and the two reportedly had an affair. But what's more surprising was the fact that Crudup was married to future "Weeds" star Mary Louise Parker at the time ... and she was pregnant.

Crudup dumped Parker for Danes during Parker's seventh month of pregnancy and the new couple dated for two years before splitting.

Brad Pitt and Angelina Jolie

Brad Pitt and Jennifer Aniston had been married for five years (which is about 50 in Hollywood years) until Pitt admitted to "falling in love" with Angelina Jolie on the set of their film "Mr. and Mrs. Smith."

Pitt and Aniston divorced in 2005 and only a month later, photos surfaced of Pitt on vacation with Jolie and her son, Maddox.

Brangelina was born.

Lauren Bacall and Humphrey Bogart

A 44-year-old Humphrey Bogart and 19-year-old Lauren Bacall met while filming "The Have and Have Not" in 1944. Bogart quickly fell for Bacall (and vice versa) and the two started having a quiet romance.

Bogart was still married to theatre and film actress Mayo Methot during that time but he finally left her to marry Bacall.

The new couple were together for 12 years until Bogart's death in 1957.